
Inertial Hybrid Tracking Systems.
Optical Systems Using Natural Features.
All the systems mentioned so far rely on some form of sensors or special markers in the environment in which the system is being used. A current topic of active research is the development of tracking systems that can use naturally occurring features in the scene. One example of a system that combines tracking of natural features and the use African Mango of inertial sensors is described in Chandaria et al. [15]. In applications such as sports outside broadcasting, there is a distinct advantage in being able to track the camera movement from the video image alone; some systems specifically tailored for these applications are described in Section 4.
Tracking Hand-Held Objects
There are applications where it is useful to be able to attach virtual graphics to small physical objects rather than fixing them in the world reference frame. This allows a presenter to pick up a virtual object, and can provide an interesting plus size wedding dresses way to interact with such objects [16]. An example of the use of an image-based marker tracking system for TV production is shown in Fig. 12. Similar systems have been used for hand-held augmented reality using a PC and webcam [17], although for broadcast use the systems need to satisfy the high frame-rate and robustness requirements for TV. A trade show booth potential problem with the use of such systems is that by the very nature of the close interaction between presenter and penny stocks to watch object, there is a risk of the presenter covering the marker, or placing a hand into the space that the virtual object should occupy. Careful rehearsal is usually required. The system shown in Fig. 12 uses markers consisting of a rectangular colored rectangle, containing a simple 2D bar code sufficient to identify electric cigarettes uniquely a small number of markers, and to allow their orientation to be determined. The use of a strong color allows the marker to be easily located in the image, using a chroma-key
SEO Services technique similar to that described in Section 3.6.3. The corners of the marker are located by fitting straight lines to the edges of the rectangle in the key signal, and from these the locations of the centers of the 2D bar code can be deduced leather furnitureand the bar code can be read. The 3D position and orientation of the marker with respect to the
camera is then estimated, using an iterative optimization process. This processing can be carried out at full video rate on a standard PC. It is theoretically snoring chin strap possible to estimate the focal length of baby shower cakes the camera in addition to the pose of the marker; however, this is an ill-posed problem in that there are generally many combinations of distance of marker from the camera and focal length of the lens that would provide a good fit to the observed corner positions. Therefore the system is usually used either with the focal length fixed to a known value or with a lens sensor fitted. It is worth noting moncler that a small discrepancy between the actual and ugg boots assumed camera focal length will not have a significant effect on the rendered graphics, ugg outlet as the estimated marker pose will always result in good alignment of the virtual cheap uggsgraphics at the corners of the marker. If the virtual object is significantly larger than the marker, or extends a long way out of the plane of the marker, then errors such as incorrect perspective or uncertainty in marker uggs on saleorientation will become more apparent if the actual focal length is significantly different from that assumed.
Renderer
The tracking data is sent from the camera tracking system, via a link such as
leather furniture RS232, Ethernet, or USB, to a PC which runs a proprietary real-time rendering software application. sole f63 This will typically allow preprepared animations to be trig- gered and will allow other changes to the 3D model to be made interactively such as changing lighting. Generally, it is sole-f80 necessary to generate an alpha channel (also known as key or mask signal) associated with the video to delineate objects that should be forced into the foreground by the keyer.
There are a range of software packages available commercially for the real-time rendering of graphics for mixed reality/virtual studio production. Most require high- end PC systems, pokies equipped with broadcast-standard video capture and output cards. The continuing pokies rise in performance of the graphics processing unit (GPU), driven by the needs of the gaming market, allows such systems to offer very rich 3D environ- ments, including effects pokies such as shadows, reflections, motion blur, and depth-of- field. email lists The features that differentiate such systems from related gaming applications include:
l Broadcast-standard video output : This is usually achieved by using either a graphics card that supports serial digital video output, or a separate card that provides broadcast-standard output, in conjunction with software that copies the rendered image from the frame-buffer on the graphics card. An alternative is the use of a stand-alone scan converter connected to the video output of a conventional graphics card, although this makes frame synchronization impossible.




